Navy Pier is taking on some additional security procedures after a melee Friday night.
Five people were arrested on charges of reckless conduct as a result of a disturbance at Navy Pier's Winter Wonderfest.
It happened Friday night a little before eight o'clock.
Police responded to a call and found about 30 people fighting.
They temporarily closed the entrance to Navy Pier at around 9 p.m.
Witnesses said they saw stampedes of high school groups running away from the Winter Wonderfest area as several fights broke out.
Saturday, Navy Pier announced visitors aged 18 and over will need to present identification, and visitors under the age of 18 will have to be accompanied by an adult.
"I express my regrets to the parents who were here and the families who were here who had to experience that. It was just absolutely ridiculous," said Navy Pier Spokesperson Nick Shields.
Navy Pier refunded people who were inside the Winter Wonderfest.
The attraction reopened Saturday afternoon with enhanced security in place.